Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$28.61	10.862%	$31.7176	$31.72	$31.70	$31.70
Purchase #2	$225.66	5.197%	$237.3876	$237.39	$237.40	$237.40
Purchase #3	$37.71	7.468%	$40.5262	$40.53	$40.55	$40.50
Purchase #4	$105.69	10.824%	$117.1299	$117.13	$117.15	$117.10
Purchase #5	$204.81	10.549%	$226.4154	$226.42	$226.40	$226.40
Purchase #6	$131.29	10.249%	$144.7459	$144.75	$144.75	$144.70
Purchase #7	$191.64	10.352%	$211.4786	$211.48	$211.50	$211.50
7 purchase totals =	$925.41		$1,009.4012	$1,009.42	$1,009.45	$1,009.30